Intro to Python basics

hello_python.py

# My comment

# Remember: use cmd i to run this file as a script

"""Style guide
module_name
package_name
ClassName
method_name
ExceptionName
function_name
GLOBAL_CONSTANT_NAME
global_var_name
instance_var_name
function_parameter_name
local_var_name

snake_case:
modules, packages, methods, functions, variables, parameters

PascalCase:
Classes, Exceptions
"""

"""
multi-line
comment
"""

# variables
fav_food1 = "sushi"
fav_food2 = "pizza"
my_number = 2**7  # 2 to the power of 7

# log or echo or print with print()
print("I love to eat {} and {}.".format(fav_food1, fav_food2))
print(f"I love to eat {fav_food1} and {fav_food2}.")

print(
    """
What's good. this is a multi line string
"""
)

# concat
print("pizza " + "sushi")
# repeat
print(3 * "yo ")
print("hey " * 3)

# strings and their characters can be treated like arrays
print(fav_food1[3])
# using a negative number starts from the end
print(fav_food1[-1])

# slicing a string using indexes
print(fav_food2[0:4])
# omit an index to assume the beginning or end
print(fav_food1[-2:])
print(fav_food2[:4])

# access the length of a string using len()
print(len(fav_food1))

# 4 space indentation for code blocks
# for loop
for val in fav_food1:
    pass

print("**** data types: boolean, number, string, tuple, list, dict ****")
# data types
# booleans
my_bool = True
my_bool = False
# numbers
integer = 123
floatingpoint = 12.3
# strings
my_string = "this is a string"
# immutable tuples -- referenced like lists
immutable_tuple = ("string", 321, True)
print(immutable_tuple[0])
# lists are basically arrays
my_list = ["some string", "some thing"]
print(my_list[1])
# dictionaries are basically objects
my_dictionary = {"name": "steve", "age": 42, "weight": 150.7, "likes_pizza": True}
print(my_dictionary["name"])

print("**** type() ****")
# find out the data type of a variable using type()
print(type(my_dictionary))
print(type(my_list))
print(type(immutable_tuple))
print("**** len() ****")
# use len() to get the length of dictionaries, lists, and tuples
print(len(my_dictionary))
print(len(my_list))
print(len(immutable_tuple))

print("**** casting: str() int() ****")
# casting a number to a string
print("Here is a number converted to a string: " + str(integer))
# casting a string to a number
string_number = "24"
print(int(string_number) / 4)


print("**** conditionals: if elif else ****")
print(f"number = {my_number}")
# conditionals
# if elif else
if my_number < 10:
    print("less than 10")
elif my_number == 10:
    print("equals 10")
else:
    print("greater than 10")

if my_number >= 100 and my_number <= 200:
    print("between 100 and 200")

if my_number == 10 or my_number > 20:
    print("is 10 or greater than 20")

if not my_number < 10:
    print("not less than 10")

if my_number != 10:
    print("is not 10")

print("**** for in loops ****")
# for in loops
for value in my_list:
    print(value)

for key in my_dictionary:
    print(f"{key}: {my_dictionary[key]}")

my_dict_keys = my_dictionary.keys()
for key in my_dict_keys:
    print(f"{key} --> {my_dictionary[key]}")

my_dict_values = my_dictionary.values()
for value in my_dict_values:
    print(value)

for key, value in my_dictionary.items():
    print(f"{key} => {value}")

print("**** range ****")
# using range
for i in range(0, 5, 1):
    print(i)

# start is inclusive
start = 1
# stop is exclusive
stop = 11
step = 1
for i in range(start, stop, step):
    print(i)

start = 5
stop = 55
step = 5
for i in range(start, stop, step):
    print(i)

# step is assumed as 1
for i in range(0, 5):
    print(i)

# start is assumed as 0
for i in range(5):
    print(i)

# break
print("**** break ****")
abbrev = ""
for char in "string":
    if char == "i":
        break
    abbrev += char
print(abbrev)

# continue
print("**** continue ****")
no_vowels = ""
for char in "mississippi":
    if char == "i":
        continue
    no_vowels += char
print(no_vowels)

print("**** while loops ****")
# while loops
count = 0
while count < 5:
    print(count)
    count += 1

print("**** while else ****")
# else in a while is like do while but in reverse, syntactically
count = 0
while count < 5:
    print(count)
    count += 1
else:
    print("else boy")

print("**** functions ****")
# function definition


def printHi():
    print("hi -- from printHi() function")


printHi()

print("**** parameters ****")


def sayHey(name):
    print(f"Hey {name}!")


sayHey("Steve")

print("**** return ****")


def add(a, b):
    sum = a + b
    return sum


print("add(3, 4) => ", add(3, 4))
total = add(16, 64)
print("total => ", total)

print("**** default parameters ****")


def sayHello(name="Jimmy", caps=False):
    greeting = f"Hello {name}!"
    if caps:
        greeting = greeting.upper()
    print(greeting)


print("**** named arguments ****")
sayHello(name="James", caps=False)
sayHello(caps=True)

print("**** multiple args using splat operator: *args ****")


def getTheSum(*nums):
    sum = 0
    for num in nums:
        sum += num
    return sum


print(getTheSum(4, 4, 8))

print("**** ternary operators ****")
# ternary --> <result_if_true> if <condition> else <result_if_false>
my_name = "David"
is_cool = True if my_name == "David" else False
print("Yeah David is cool" if is_cool else "Nah that person ain't cool")

print("**** lambdas ****")
# a lambda is an anonymous function
print(list(map(lambda x: x**2, [1, 2, 3])))

print("**** classes ****")


class Person:
    def __init__(self, name, age, city):
        self.name = name
        self.age = age
        self.city = city


steve = Person("Steve", 25, "Boise")
jen = Person("Jen", 35, "Brooklyn")
print(f"{steve.name} is {steve.age} years old and lives in {steve.city}")
print(f"{jen.name} is {jen.age} years old and lives in {jen.city}")

print("**** methods ****")


class House:
    def __init__(self, color="purple"):
        self.color = color

    def paint(self, color):
        self.color = color


my_house = House("teal")
print("My house is painted ", my_house.color)
my_house.paint("yellow")
print("Now my house is painted ", my_house.color)

print("**** encapsulation ****")


class Family:
    def __init__(self, members=[steve, jen]):
        self.members = members
        self.house = House()

    def printPaint(self):
        print(self.house.color)

    def printMembers(self):
        for member in self.members:
            print(f"{member.name} is {member.age} years old.")

    def addMember(self, member):
        self.members.append(member)


my_family = Family()
my_family.addMember(Person("Alicia", 30, "San Fran"))
my_family.printPaint()
my_family.printMembers()

print("**** chaining methods ****")


class Maths:
    def __init__(self):
        self.result = 0

    def add(self, *nums):
        for num in nums:
            self.result += num
        return self

    def subtract(self, *nums):
        for num in nums:
            self.result -= num
        return self


my_maths = Maths()
print(my_maths.add(4, 8).subtract(2, 2).add(4, 4, 4).result)
print(my_maths.add(2).add(2, 5, 1).subtract(3, 2).result)

print("**** the end ****")

Python → let's learn it

This one goes out to all the homies who are juuusssttt getting started learning Python.

• Python Docs
• Tutorial
• Python Library
• Reference
• w3schools intro
• BeginnersGuide
• SimpleExamples
• Overview
• Glossary

Cheat sheets (as PDFs):

• https://perso.limsi.fr/pointal/_media/python:cours:mementopython3-english.pdf
• https://s3.amazonaws.com/assets.datacamp.com/blog_assets/PythonForDataScience.pdf
• https://s3.amazonaws.com/dq-blog-files/python-cheat-sheet-basic.pdf